Each new President and congressional committee wants to give them something new to shoot for and then never really gives them the funding to be able to reach those goals. So, every few years they have to rearrange what they have been planing for 8 years or more to suit the new party in charge. If we had just given them a fraction of the military's budget and then let them decide on what goals they want to make we would probably already have a international moon base and have cheaper fuel on hand to experiment in our solar system till the scientists and explorers heart was content.